Not applicable.
The present invention relates to a process for the hydrogenation of carbon monoxide to produce hydrocarbons and/or oxygenates. More particularly, the present invention relates to the use of an aluminum borate supported Fischer-Tropsch catalyst. Still more particularly, the present invention relates to the use of a cobalt or a promoted cobalt Fischer-Tropsch catalyst on an aluminum borate support.
Large quantities of methane, the main component of natural gas, are available in many areas of the world. However, most natural gas is situated in areas that are geographically remote from population and industrial centers. The costs of compression, transportation, and storage make the use of this remote gas economically unattractive. To improve the economics of natural gas use, much research has focused on the use of methane as a starting material for the production of higher hydrocarbons and hydrocarbon liquids.
As a result, various technologies for the conversion of methane to hydrocarbons have evolved. The conversion is typically carried out in two steps. In the first step, methane is reformed with water or partially oxidized with oxygen to produce carbon monoxide and hydrogen (i.e., synthesis gas or syngas). In a second step, the syngas is converted to hydrocarbons.
This second step, the preparation of hydrocarbons from syngas, is well known in the art and is usually referred to as Fischer-Tropsch synthesis, the Fischer-Tropsch process, or Fischer-Tropsch reaction(s). The Fischer-Tropsch reaction involves the catalytic hydrogenation of carbon monoxide to produce a variety of products ranging from methane to higher aliphatic hydrocarbons and/or alcohols. The methanation reaction was first described in the early 1900""s, and the later work by Fischer and Tropsch dealing with higher hydrocarbon synthesis was described in the 1920""s.
The Fischer-Tropsch synthesis reactions are highly exothermic and reaction vessels must be designed for adequate heat exchange capacity. Because the feed streams to Fischer-Tropsch reaction vessels are gases, while the product streams include liquids, the reaction vessels must have the ability to continuously produce and remove the desired range of liquid hydrocarbon products. The first major commercial use of the Fischer-Tropsch process was in Germany during the 1930""s. More than 10,000 B/D (barrels per day) of products were manufactured with a cobalt based catalyst in a fixed-bed reactor. This work was described by Fischer and Pichler in Ger. Patent 731,295 issued Aug. 2, 1936.
Motivated by the hope of producing high-grade gasoline from natural gas, research on the possible use of the fluidized bed for Fischer-Tropsch synthesis was conducted in the United States in the mid-1940s. Based on laboratory results, Hydrocarbon Research, Inc. constructed a dense-phase fluidized bed reactor, the Hydrocol unit, at Carthage, Tex., using powdered iron as the catalyst. Due to disappointing levels of conversion, scale-up problems, and rising natural gas prices, operations at this plant were suspended in 1957. Research continued, however, on developing Fischer-Tropsch reactors, such as slurry-bubble columns, as disclosed in U.S. Pat. No. 5,348,982. Despite significant advances, however, certain areas of Fischer-Tropsch technology still have room for improvement.
Catalysts for use in the Fischer-Tropsch synthesis usually contain a catalytically active metal of Group VIII. In particular, iron, cobalt, nickel, and ruthenium have been used as the catalytically active materials. Nickel is useful for a process in which methane is a desired product. Iron has the advantage of being readily available. Ruthenium has the advantage of high activity and thus is typically used a promoter for another of the catalytic materials, due to the limited availability of ruthenium. Cobalt has the advantages of being more active than iron and more available than ruthenium. Further, cobalt is less selective to methane than nickel. Thus, cobalt has been investigated as a catalyst for the production of hydrocarbons with weights corresponding to the range of the gasoline, diesel, and higher weight fractions of crude oil.
Additionally, the catalysts often contain one or more promoters and a support or carrier material. Research is continuing on the development of more efficient Fischer-Tropsch catalyst systems and catalyst systems that increase the activity of the catalyst. In particular, catalyst supports that have been investigated include ceramic supports. Ceramic supports include various structural forms of alumina, such as alpha and gamma alumina, in addition to silica, titania, zirconia, zeolites, spinels, sol-gels, co-gels, and the like. It is known that the catalyst activity can vary with the composition and structure of the support.
Despite the vast amount of research effort in this field, Fischer-Tropsch catalysts supported on current ceramic supports are not always sufficiently active. Hence, there is still a great need to identify new catalyst supports, particularly catalyst supports that result in improved catalyst activity and thus enhance the process economics.
This invention relates to a process and catalyst for producing hydrocarbons, and includes a catalytically active material containing cobalt and a catalyst support containing aluminum borate. The Fischer-Tropsch synthesis process includes contacting a feed stream comprising hydrogen and carbon monoxide with this supported catalytic material in a reaction zone maintained at conversion-promoting conditions effective to produce an effluent stream including hydrocarbons.
The present catalyst preferably comprises a support including from about 20 to about 60 wt % aluminum, from about 0.5 to about 10 wt % boron, and from about 40 to about 70 wt % oxygen. The present catalyst preferably further contains a catalytically active material including from about 10 to about 25 wt. % cobalt, and preferably also includes a promoter in a concentration sufficient to provide a weight ratio of elemental promoter to elemental cobalt between about 0.0001 and about 0.5. The promoter is chosen from Groups 1-11 and 13 of the Periodic Table New Notation). Less preferred promoters are selected from Groups 12 and 14. The support preferably includes 2 to 5 wt % boron and the catalyst preferably includes 10 to 25 wt % cobalt.
In a particular aspect of the present invention, the catalyst is prepared by a method including impregnating alumina with a boron-containing composition to form an aluminum borate support; and impregnating the aluminum borate with a composition comprising cobalt and optionally rhenium to form a supported catalyst. The resulting catalyst system is adapted to hydrogenate carbon monoxide.
In another aspect of the present invention, the aluminum borate support is used in a catalyst system for the production of hydrocarbons in a process that includes contacting a feed stream including hydrogen and carbon monoxide with the catalyst system in a reaction zone maintained at conversion-promoting conditions effective to produce an effluent stream comprising hydrocarbons.
The process and catalyst of the present invention have the advantage of being adapted to provide superior catalytic activity, in particular as compared to a catalyst having the same catalytically active material composition on a conventional alumina support.